Infrared search and track

[2] The IRST was also incorporated into the F-8 Crusader (F-8E variant) allowing passive tracking of heat emissions and was similar to the later Texas Instruments AN/AAA-4 installed on early F-4 Phantoms.

It was not not installed on later F-4Ds due to limited capabilities,[5] but retained the bulge and indeed some F-4Ds had the IRST receiver retrofitted in a modified form.

IRST systems re-appeared on more modern designs starting in the 1980s with the introduction of 2-D sensors, which cued[clarification needed] both horizontal and vertical angle.

[12] The United States Air Force is currently incorporating IRST systems for its fighter aircraft fleet, including the F-15, F-16, and F-22.

Any IR light falling on the sensor would generate a "pip" on the display, in a fashion similar to the B-scopes used on early radars.

The system was considered to be of limited utility, and with the introduction of more automated radars they disappeared from fighter designs for some time.

Detection range varies with external factors such as The higher the altitude, the less dense the atmosphere and the less infrared radiation it absorbs - especially at longer wavelengths.

An IRST system may also have a regular magnified optical sight slaved to it, to help the IRST-equipped aircraft identify the target at long range.

IRST systems can incorporate laser rangefinders in order to provide full fire-control solutions for cannon fire or launching missiles (Optronique Secteur Frontal).